Vasopressin (AVP) is a peptide produced in the brain and released both centrally and peripherally. The central actions of AVP include effects on both social and non-social behaviors. Two main subtypes of AVP receptors exist in the brain, namely V1alpha and V1beta. It is unclear via which receptor subtype AVP acts to affect these behaviors. Understanding the mechanisms behind AVP's effects on anxiety and social recognition is particularly important given the relationship between these behaviors and human disorders such as anxiety disorder and autism. The aims of this proposal are to use mice with a null mutation in the V1alpha receptor (V1aRKO) to better understand how AVP affects anxiety and social behavior. In the first aim, the V1aRKO mice will be behaviorally and neurochemically phenotyped to assess the effects of a null mutation in the V1aR. In the second aim, differences in c-fos-IR between the V1aRKOs and WT animals will be used to determine neuroanatomical regions involved in anxiety and social behavior. In the third aim, a V1aR viral vector will be used to re-express the V1aR in specific neuroanatomical regions, in an attempt to alter the anxiety and social behavior of the KO mice. These experiments will further our understanding of the mechanisms involved in AVP mediated anxiety and social behavior. [unreadable] [unreadable]